Smoking of tobacco products produces three types of smoke, namely mainstream smoke, exhaled smoke and sidestream smoke, particularly as it would relate to the smoking of cigarettes. Filter materials abound for use in removing sidestream smoke and exhaled smoke in somewhat confined areas where people might be smoking. It is generally understood that sidestream smoke accounts for the majority of smoke emitted during the smoking process. There has therefore been significant interest in reducing sidestream smoke and this might be accomplished by one or more of the following techniques:                i) alter the tobacco composition and packing characteristics of the tobacco rod charge in the cigarette or cigar;        ii) alter the cigarette paper wrapping of the cigarette or cigar;        iii) alter the diameter of the cigarette as well as its tobacco composition and/or provide a device on the cigarette or cigar to contain and/or control sidestream smoke emissions.        
Various cigarette tobacco and cigarette paper designs have been suggested with a view to reducing sidestream smoke. In one way or another these designs affect the free-burn rate of the cigarette or cigar resulting in an extinguishment of the lit cigarette or cigar when left idle over an extended period of time. Such designs include a selection of tobacco blends, smaller cigarette diameters, densities and multiple layers of cigarette tobacco in the tobacco charge. Such selected designs can appreciably retard the free-burn rate of the cigarette and hence, increase the number of puffs obtained per unit length of cigarette. Either in combination with tobacco selection and/or construction or independently of the tobacco make up, various cigarette paper compositions can also affect free-burn rate of the cigarette. Such paper compositions include the use of chemicals to retard free-burn rate, chemicals to reduce sidestream smoke, multiple wrappings of different types of cigarette paper of the same or different characteristics and reduction of air permeability. See for example, Canadian Patents 1,239,783 and 1,259,008 and U.S. Pat. Nos. 4,108,151; 4,225,636; 4,231,377; 4,420,002; 4,433,697; 4,450,847; 4,461,311; 4,561,454; 4,624,268; 4,805,644; 4,878,507; 4,915,118; 5,220,930 and 5,271,419 and U.K. patent application 2,094,130. Cigarettes of smaller diameter have also been tried such as described in U.S. Pat. No. 4,637,410.
Various devices have been provided which contain the cigarette, primarily for purposes of preventing accidental fires. They may or may not at the same time include various types of filters to filter and thereby reduce the amount of sidestream smoke. Examples of such devices are shown in U.S. Pat. Nos. 1,211,071; 3,827,444; 3,886,954 and 4,685,477.
Further, various types of cigarette holders have been made available which serve the primary feature of minimizing staining of the smoker's fingers. Such devices may be connected to the cigarette tip and/or mounted on the cigarette, such as shown in U.S. Pat. No. 1,862,679. Other types of cigarettes which are enclosed in wrappers which are perforated in one way or another to provide for safety features and/or control of sidestream smoke are described in Canadian Patent 835,684 and U.S. Pat. Nos. 3,220,418 and 5,271,419.
Devices which are mountable on the cigarette and which may be slid along the cigarette to control rate of combustion and hence free-burn rate are described in U.K. patent 928,089; U.S. Pat. No. 4,638,819 and International application WO 96/22031. U.K. patent 928,089 describes a combustion control device for cigarettes by limiting the flow of air to the cigarette burning ember. By retarding combustion of the cigarette, it is suggested that only half of the conventional amount of tobacco need be incorporated in the cigarette and result thereby in a shorter cigarette. The air flow limiting device may be provided by an array of apertures in the device with variable opening or by crimped portions in the device providing longitudinal openings along part of the cigarette. U.S. Pat. No. 4,638,819 describes a ring which is placed on the cigarette and slid therealong during the smoking process to control the free-burn rate of the cigarette and reduce sidestream smoke. The ring is of solid material, preferably metal, which causes considerable staining and due to variable cigarette diameters cannot reliably provide the desired degree of sidestream smoke reduction and extinguishing times.
Other systems, which have been designed to control sidestream smoke, are described in International application WO 95/34226 and U.S. Pat. Nos. 4,685,477; 5,592,955 and 5,105,838. These references describe various tubular configurations in which a tobacco element is placed in an attempt to minimize cigarette sidestream emission.
Various types of ceramic constituents have been used in cigarette structures including insulating tubes for cigarettes as well as insulating tubes for cigarette smoke aerosol generating devices. U.S. Pat. No. 4,915,117 describes a thin sheet of ceramic, which is substituted for cigarette paper to reduce organic substances given off during the burning of conventional cigarette paper. Insulated ceramic sleeves are described in U.S. Pat. Nos. 5,105,838 and 5,159,940. U.S. Pat. No. 5,105,838 describes a cigarette unit having a thin tobacco rod of a circumference of about 12.5 mm. The insulating ceramic sleeve has low heat conductivity and is porous. In order to achieve reduction in sidestream smoke emissions from the burning tobacco rod, the free-burn rate is reduced by the use of a low porosity wrap over the porous ceramic element where the wrap has a permeability less than about 15 Coresta units.
U.S. Pat. No. 5,592,955 describes a porous shell which is re-usable and non-combustible for concealing and retaining a rod of smokable material before, during and after smoking. Reduction of sidestream smoke emitted from this device is provided by an outer wrap for the shell which has a permeability of less than 40 Coresta units where the shell has a radial thickness of about 0.25 mm to 0.75 mm. The wrap controls the overall porosity of the device and thereby controls free-bum rate of the cigarette and reduces sidestream smoke developed during intervals between puffs. The device includes an air permeable cap at the open end of the tube. The non-combustible shell may include bands of metal which act as heat sinks to reduce the free-burn rate of the tobacco rod.
Catalytic materials have been used in smoking devices such as in the tobacco and particularly in cigarette smoke filters to convert mainstream smoke constituents usually by oxidation as taught in U.S. Pat. No. 3,693,632; U.K. Patent 1 435 504 and published European patent applications EP 107 471 and EP 658 320. Catalysts have also been included in cigarette papers for wrapping tobacco such as described in Canadian Patent 604,895 and U.S. Pat. Nos. 4,182,348 and 5,386,838. Adsorptive materials, such as zeolites have been incorporated in the tobacco as well as the cigarette filter. Zeolites adapted for this use are described in published European patent application EP 740 907, where such zeolites have pore sizes within the range of 5 to 7 Å.
The applicant has made a considerable contribution in this area, as described in its U.S. Pat. Nos. 5,462,073 and 5,709,228 and International applications WO 96/22031; WO 98/16125 and WO 99/53778. The non-combustible systems described in each of these published patents and applications are directed towards cigarette sidestream smoke control systems. In particular, International application WO 99/53778 is directed to a cigarette sidestream smoke treatment material which is based on the combination of the material having a highly porous structure well in excess of 200 Coresta units and an oxygen storage component with oxygen donating ability. Although these various devices have met with varying degrees of success in controlling sidestream smoke emissions from a burning cigarette, the various embodiments of this invention provide a non-combustible smoke treatment material that is capable of treating cigarette tobacco sidestream smoke in a surprisingly superior manner, without the need for a highly porous material to encourage the conventional free-burn rate. Specifically, this invention is directed to a more easily manufactured, non-combustible sidestream smoke treatment material having a porosity less than about 200 Coresta units.